#### 15.7.3 Limiting bitmap resolution and color depth

Graphics destined for print look best at a resolution of 300 to 1,200 DPI. However, you cannot increase the DPI of an existing bitmap image: the upper limit of resolution is the DPI of the original graphic.

Use 256-color (8-bit) BMP images where possible

The number of colors in bitmap images should be 256 or less, because the size increase for more colors can make files too large for Word to load. If you use 24-bit color, conversion can be slower and the resulting .rtf files much larger. This is because DITA2Go has to use embedded WMFs to get the images into Word, and 24-bit bitmaps do not compress in WMFs. If you are using 256 colors (8-bit bitmaps), conversion is faster and output file size smaller. However, reducing a photographic image to 256 colors degrades its appearance.

Save Word files with 24-bit BMP images as .doc

RTF lacks compression for 24-bit BMP images (which include “millions of colors”). Every pixel takes 3 bytes. At 300 DPI for acceptable print quality, a 3.25" x 3.5" image would contain 1,023,750 pixels, requiring about 3 MB in a binary format. However, because RTF represents each byte with two hexadecimal digits, the actual size would be 6 MB. On the other hand, if you are able to load an RTF file containing such an image into Word, you can save the file as a Word .doc file. Then Microsoft uses a proprietary compression method to shrink the size drastically. Unfortunately, DITA2Go cannot legally use this method, thanks to the Digital Millennium Copyright Act (DMCA).

Previous Topic: 15.7.2 Understanding where to locate graphics

Next Topic: 15.7.4 Preserving graphics scale in Word

Parent Topic: 15.7 Managing graphics for print RTF

Sibling Topics:

15.7.1 Understanding graphics requirements for Word

15.7.2 Understanding where to locate graphics

15.7.4 Preserving graphics scale in Word

15.7.5 Accommodating graphics in multiple versions of Word

15.7.6 Including file names of referenced graphics in Word

15.7.7 Linking instead of embedding referenced graphics

15.7.8 Embedding graphics in converted RTF files

15.7.9 Updating fields in Word to show linked graphics